1. Field Of The Invention
Embossing with a rolling contact machine using a rotary die.
2. Description of the Prior Art
In most embossing operations, it is desirable that the material being treated receives a pattern of uniform depth and quality on both sides. Heretofore, this desiderata has been obtained by either utilizing mating male and female dies or running the material twice through an embossing machine comprising either an engraved embossing roll and a resilient backup roll or an engraved embossing roll bearing against a resilient blanket or belt supported by a hard surfaced backup roll. For a more complete discussion and example of prior art embossing machinery reference is made to U.S. Pat. Nos. 389,949; 2,611,312; and 3,247,785. The first of these, U.S. Pat. No. 389,949 to J. M. Baker, shows an embossing machine wherein the engraved embossing roll bears against an elastic belt of soft rubber supported by a backup roll. With this type of construction, it is believed, in order to obtain uniform embossing on both sides of the web, it is necessary to direct the web through the embossing nip in at least two passes.
In U.S. Pat. No. 2,611,312 uniform embossing on both sides of the web is obtained by running the web through a calender stack having two engraved embossing rolls. Of course, a machine of this type, would be quite expensive and cumbersome and not suited for many installations.
U.S. Pat. No. 3,237,785 to R. S. Shultz, utilizes a thin resilient covering of 1/32 inch on a hard surface backing roll. As an embossing technique for aluminum foil, the Shultz disclosure may be considered successful since sharp relief may be transferred to both sides of the web in a single pass. However, aluminum requires only 2% of the nip pressures required by paper. Under the moderate to high nip pressures required for double face paper embossing, the thin, resilient backing layer 56 experiences stress distortion of such magnitude that it is extremely difficult, if not impossible, to hold the backing layer tightly and smoothly against the backing roll 47. Consequently, as a commercial method for embossing paper, the Shultz apparatus is unacceptable. Although numerous valcanizing and bonding techniques have been attempted, no successful method has been found to prevent the thin backing layer 56 of Shultz from distorting beyond the yield limit of such bonds. In a relatively short interim at 600 pounds per lineal inch (pli) nip pressure operating on paper, a backing layer of the type and dimension described by Shultz will be torn from the steel backing roll 56.